A variety of substrates and hormones can alter the rate of protein degradation in skeletal and cardiac muscle. However, the mechanism(s) by which these substances regulate proteolysis remain unknown. It is proposed in this application that the reduction-oxidation state (or potential) of the cell may provide a common element for the ultimate regulatin of proteolysis in the muscle. To evaluate this hypothesis, the effect of various substrates (e.g. leucine, glucose) and hormones (e.g. insulin, cortisol) on the oxidation state of the NAD, NADP and glutathione couples will be tested in incubated skeletal and cardiac muscle preparations from rats. These results will be compared with the influence of these substances on protein degradation. Like other degradative pathways, proteolysis may proceed more rapidly under more oxidized conditions. Activities of muscle proteinases (e.g. cathepsins B and D, Ca2+-activated proteinase) will be assayed in homogenates of muscles pre-incubated under these same experimental conditions. Artificial alterations of the reduction-oxidation state and the resulting effects on proteolysis will be studied. Other experiments will attempt to correlate metabolic alterations in the intact animal (e.g. adrenalectomy, thyroidectomy) with changes in muscle protein breakdown. Additional in vivo and in situ analyses will be carried out to demonstrate the physiological significance of the in vitro observations. Since excessive degradation of muscle protein is evident in a variety of disease states (e.g. muscular dystrophy, diabetes, trauma), the demonstration of proteolytic regulation by the reduction-oxidation potential could provide important information for understanding better the response of muscle to these abnormal conditions. Therefore future studies will utilize diabetic and dystrophic animals to examine the possibility that the accelerated degradation of their muscle proteins may be due, at least in part, to an altered reduction-oxidation state relative to normal animals. If this mechanism for controlling muscle proteolysis proves to be physiologically significant, it could lead possibly to procedures for lowering the rate of protein degradation in disease states.